Process for purifying coal gases



Patented June 27, 1933 i PATENT.OFFICE V rmrz'ovnnnrox, OF HULS,GERMA1\TY, Assrenon '10 1e. rnnnnninnnsrnrnfnmrnn n eEsnLLsoHArT, onrnAnnronnon-Tnn-MAIn; QERMANY,,IA 'CORPORATION on fixing the hydrogen cyanide and, after boil-L ing, separating from the resulting wash GERMANY The present invention concernsa process for the simultaneousremoval of ammonia, hydrogen sulfide and hydrogencyanidefroml gases with the recovery "of ammoniumsu fate, sulfur and 'ammoniumthiocyanate by means of wash liquors containing ammonium} polythionateand ammonium thiosulfate and;, consists in addingvto the wash liquors, besides the quantity ofammonia necessary to complete absorption of: the hydrogen sulfid the'requisite amount of ammonia needed forg,

liquor the ammoniumsulfate and ammonium thiocyanate by fractional evaporation. In removing ammonia and hydrogen sul-, fide from gases by means ofammonium poly-j thionate solutions, it has hitherto been necessary lfirstto removethe hydrogen cyanide from the gas, since this, according to the prevailing conditions, was also more or less absorbed with the formation of ammonium thiocyanate, thereby contaminating the ammo nium sulfate obtained. Y f p I In accordance with the present invention, ammonia, hydrogen sulfide and hydrogen cyanide are simultaneously and completely maintained weakly alkaline,'that is to say,

removed from the gases by means of poly thionate, solutions without a preliminary 11y-v drogen cyanide Washing, whilst the products obtained are separated from one anotherfin the most simple manner.v f

The first part of the. process, the absorption of 'hydro'genycyanide besides hydrogen sulfide by polythionate solutions, onlyproceeds' quantitatively, when the ,liquor is when the wash liquor contains, in addition to the quantity oi ammonia necessaryfor atom plete absorption of the hydrogen sulfide, such additional ammonia as is needed for the for-. mation of the ammonium thiocyanate produced in the hydrogen cyanide absorption z+- NHg-t HCN-l- (NI- 8 05; F 1 v a i 1 NH GNS l-(N'HQ S OQ As has also been established (U; S. Patent 1,826,779), a quantitative absorption of by drogen sulfide is only achieved, when more than two molecules of ammonia are added to the polythionate solution for each molecule ritoenss e PURIliYiNG Conn GASES ot fhydrogen; sulfide to be absorbed. The

requisiteratio of ammonia to hydrogcnsulfide depends on the conditions of working and ,isjv in general about 2,3 1no1ecules of amnonia to onemolecule of hydrogensulfide,

Thus: for the hydrogen cyanide absorption one moleculeof ammonia mustlhe added to each molecule of hydrogen cyanide over and above his proportion. Since, however, in most cases the ammonia content. of the gas does not suflacking must be made up from other sources In order to carry out the process. The same:

No Drawing". Application filed December 19, 1928, Seria1 No. 327,194, and in Germany December 21, 1 927."

60 fice for this purpose, the quantity of ammonia applies in every case to the sulfur, the quan-' tity ofwhich must be replenished at the rate at whichthe quantityof ammonia exceeds theratio of two molecules of ammonia to one molecule of hydrogensulfide. a

Theiollowfng examples serve toillustrate our invention without ,limiting it thereto. The percentagesstated therein are percents ages-by Volume." j v v i a v Eazample '1,'- The crude gas contains on an of hydrogen sulfide and 0,1 per cent of. hy{ vdrogen cyanide. ,The complete absorption of the hydrogen sulfide is presumed to require for each molecule of hydrogen sulfide about 2,3) molecules of ammonia, that is to say in, this case, l,8 lc per cent [of ammonia. To this 'hasfto -b e added 10,1, per cent neededfor fixing' the hydrogen cyanide, so

average 1,2 per cent of'ammonia, 0,8 per cent that for carrying out the process 1,9 1 per cent of ammonia is required} Thus there is lacking, (1.945 1.2) per cent of arm monia and; I 1

centjoii acid onsulfuriithat The process 1n question can be carried out in a: more economical'mann er w1th1, th 'equansets of ammoniajand sulfur, occurringIinv the gas by utillzmg the combination 'd'e scribed in the applicationSer, No. 286,712,",

in which case the absorption of hydrogen Y Y 1 cyanide'is carriedout in the second. stage of the process by then adding a quantity of ammonia equivalent to the hydrogen cyanide or alternatively precipitating in the first stage a corresponding amount of hydrogen sulfide.

EwampZe2.The proportions of gas are as in Examplel that is to say:1.-.2.. ,per cent of ammonia are available for the second stage with which 0.52 per cent of hydrogen sul-.

fid m Washed Qut a-th tQ- 8 p sen of hydrogen sulfide mustbe remOWedYin the first stage. Since however in the second stage 0.1 per cent of ammonia is consu-med in the hydrogen cyanide absorption only Qtfil percentof hydrogen sulfide can be-.,ab 1 sorb-ed by the remaining 1.1 per cent of ammonia. Therefore 0.32 per c entfofhydrogen sulfide .must be removed inthepreliminary stage.

As has already been said it was indeed known thatpolythionate reacts with hydrogen cyanide, nevertheless the utilization of this fact for technical working has never been contemplated, since it is the present invention which'first develops'the complete absorption of cyanogen under the conditions herein described and moreover no. means were available of working up the wash liquors obtained.

The separation of the ammonium thiocyanate from the other salts of the wash liquor constitutes the second part'of the process. For this purpose the liquor containing ,chiefiy ammonium vpolythionat'e,

thiosulfate and ammoniumthiocyanate is boiled in the known'man'ner so that, after filtration from the separated sulfur, it only contains ammonium sulfate and ammonium thioyanatei These two salts can be easilyand completely separatedtechnically by fractional evaporation. The solubility of ammonium sulfate is reduced by the presence of ammonium thiocyanate to such an extraordinary extent, that on evaporation of the liquor ammonium sulfate'is almostcompletely precip1tated "before the separation of monium thiocyanate begins. Conversely there ;is obtained finally a saturated an} "moni'um thiocyanate solutionionly slightly contaminated withiammonium sulfate. Since ammonium thiocyanate is extremely easily soluble, the impurities, even when calculated on the dry salt, are only insignificant, all the more'so, thehigher the evaporation temr ta e has b en Since th amm nium thiocyanate content of a solutionsaturated w th bo al uses ry rap d y W t th temperature While under'the sameconditions the sulfate cont-enteven falls little further. I

. The combination CfJSlIlS method of working 7 with the absorption described above constiatmospheric 'pressure.

tutes an entirely new process for simulta neously purifying gases, from ammonia, hydrogen sulfide and hydrogen cyanide, the products'of the purification being obtained in the form of ammonium sulfate, sulfur and ammonium thiocyanate. A great advantage of theprocess is to be found in the fact that a separate hydrogen cyanide washing and 'tit e Wit separat nn s-m i wa fle that moreover the large absorption capacity of the liquor for hydrogen cyanide renders ;possible,a completepurification. The evaporation of the boiled wash liquor is likewise carried out without further. expense, since ,fractionating only takes place towards the end of the evaporation.

The process can be carried outu nder super- "I claim v v 1 Process which comprises washing crude coal gases with wash liquors containing ammonium polythionate and ammonium thiosulfate and such a quantity of free ammonia asis necessary "for the complete removal of hydrogen sulfide and hydrogen cyanide, boiling the resulting liquors, separating the sulfur obtained and fractionally evapo'rating the ammonium .sulfate and ammonium 'thiocyanate containingliquor.

2. Process which comprises washing crude coal gases with wash liquorscontaining ammonium polythionate and ammonium thiosulfat e and'sucha quantity of free ammonia as is necessary for the complete removal of hydrogen sulfide and hydrogen cyanide, boilnewths r su in il quors, sepa at the sulu sb ained and ra i a ly e po a n the ammonium sulfate and ammonium thiocyanate containing liquorunder superatmose as s necessary for thei complete ,rempv i of hydrogen, ulfide and hydrogencyanide a der superatmospheric pressure. In testimony whereof I have hereunto set I FRITZ .OYERDICK. [1 a] 

